1. Field of the Invention
The present invention relates to an autamatic focusing lens which can be switched between an automatic focusing operation (hereinafter refered to as AF) mode and a manual focusing operation (hereinafter refered to as MF) mode.
2. Description of the Related Art
Conventionally, a camera having an automatic focusing lens which can be switched between an AF mode and an MF mode is known. The automatic focusing lens is provided with a drive shaft which, in the AF mode, is connected to a motor housed in the camera body to move a lens along the optical axis. In the MF mode, the drive shaft is disconnected from the motor so that the lens can be manually moved.
In such an automatic focusing lens, a focusing operation in the AF mode should be carried out at a high-speed, and an electric power consumption of the motor should be low, and therefore, a drive force for displacing the lens in the optical axis must be made as small as possible, to ensure a smooth movement of the lens.
If the drive force for displacing the lens along the optical axis is lowered, however, the lens can also be moved along the optical axis by a small force in the MF mode, and thus the operability of a manual focusing operation is not good. Especially, when carrying out close-up photography with a macro lens, the lens may be displaced along the optical axis by the weight of the lens, and thus may be unwantedly moved out of focus.
On the other hand, in a lens such as a macro lens in which a displacement amount along the optical axis during a focusing adjustment is large, the amount of displacement of the lens must be reduced for an AF operation, so that the lens does not repeat a movement along the optical axis in the AF operation. Accordingly, in the AF operation, the photographing mode must be switched between a full range automatic focusing adjustment in which an automatic focusing operation is carried out in a range between a shortest photographing distance and infinity, and a restricted automatic focusing adjustment in which an automatic focusing operation is carried out in a range between a shortest photograping distance and a predetermined photographing distance or between the predetermined photographing distance and infinity.
In an automatic focusing lens having a mechanism for switching between an AF mode and an MF mode, and a mechanism for switching between the full range automatic focusing adjustment and the restricted focusing adjustment, if separate mechanisms are provided for carrying out each switching operation, a large space is needed in the automatic focusing lens, and the construction thereof is complicated, and further, the switching operations are complicated.